Mashup
A mashup combines recognizable elements from two or more existing recordings so they function together—often a vocal from one over the instrumental framework of another. The relationship between sources is the central idea.
Remix
A remix reworks one primary recording. It may change the beat, arrangement, length, genre or emphasis while remaining centered on that source. Official remixes are commonly made from provided stems; unofficial remixes raise separate permission questions.
Medley
A medley places songs one after another, usually through transitions or condensed sections. The songs may overlap briefly, but they do not need to operate simultaneously. A DJ set can contain medleys, remixes and mashups in the same sequence.
Why the label matters
Clear terminology helps listeners understand the craft and helps creators credit sources accurately. It does not decide the legal status of a work; rights depend on what material is used, how it is used and where it is distributed.